<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 
        .box div class为box的所有后代div元素
        .box > div class为 box 的下一级子元素的div元素
         */
        .box > div{
           width: 100px;
           height: 100px;
        }
        input[name=test]:focus{
            color: red;
            border: 5px solid #aaa;
        }
        .test-element:active{
            color: red;
        }
        /* 超链接未被访问过 */
        a:link{
            color: blue;
        }
    </style>
</head>
<body>
    <div class="box">
        <div>
            这是子元素div
            <ul>
                <li>
                    <div>
                        这是li中的div
                    </div>
                </li>
            </ul>
        </div>
    </div>

    <input name="test" type="text">
    <div class="test-element">这是测试元素</div>
    <!-- <a href="www.baidu.com" target="_black">这是超链接</a> -->
    <a href="#" >11</a>
</body>
</html>